Explosive rivet



June 12, 1951 A, BURROWS ETAL 2,556,465

EXPLOSIVE RIVET Filed May 25, 1945 Lawton A Builows Wa l Zer" ll -L aWson ATTORNEY IN V EN TORS Patented June 12, 1951 EXPLOSIVE RIVET Lawton A. Burrows, Woodbury, N. J and Walter E. Lawson, Wilmington, Del., assignors to E. I. du Pont de Nemours 85 Company, Wilmington, Del., a corporation of Delaware Application May 25,1945, Serial No. 595,738

This invention relates to an improved rivet intended for securing together superposed sheets of material or other objects and containing within a cavity in said rivet an explosive charge adapted on explosion to bulge the side walls and thereby efiect a firm gripping of the sheets.

The present application is an improvement of our co-pending application, Serial No. 426,150 filed January Q, 1942, which application was issued on October 29, 1946 as Patent Number 2,410,047. I

Explosive rivets have become a highly important aid to industry within the past few years and are applicable in many places where the ordinary type of rivet cannot be used, particularly in uses where access to one side is difiicult or impos sible. Explosive rivets comprise ordinarily metal fastening devices having a head and a shank, the shank being provided with a cavity into which an explosive charge is loaded. Customarily the cavity extends slightly beyond the far edge of the second plate to be secured. The charge is detonated by application of a heated surface to the head of the rivet whereby the entire rivet becomes heated above the firing temperature of the explosive. At the moment of explosion, the Walls of the rivet become expanded or bulged so that the metal sheets to be joined become firmly held together.

Rivets of the explosive type have given very successful results when used under suitable conditions. They have not been entirely satisfactory, however, under certain circumstances, especially where the rivets were inserted into somewhat oversize holes such as would give easier and speedier rivet insertions.

An object of the present invention is an improved explosive rivet efiecting tighter and stronger joints than prior art rivets of this type and applicable under conditions where unsatisfactory results have previously been obtained. A further object is such a rivet .so. designed at to allow a more efficient loading of the explosive charge. A still further object is an explosive rivet affording tighter junctions where therivets are used in holes allowing considerable clearance. Additional objects will be disclosed as the invention is described more at length in the following.

We have found that the foregoing objects are accomplished, and the disadvantages encountered with prior art devices overcome, when we employ a rivet having a cavity extending longitudinally through a substantial part of the shank, and desirably entering from the shank 1 Claim. (CI. 8540) 2 end, this cavity comprising a main portion of a diameter between 0.4 and 0.6 of that of the shank and an extended portion of a substantially smaller diameter than that of the main portion. A preferred diameter for the extended portion is between 02 and 0.4 of the diameter of the shank. Desirable results are obtained when this portion of reduced cross section extends substantially to the head of the rivet. The charge will be so loaded that the increment in the main cavity is at least slightly beyond the further surface of the second sheet to be joined while the portion in the cavity extension of reduced diameter blasts the rivet metal into tight connection with the walls of the metal through which the rivet is inserted.

Rivets constructed in accordance with the present invention are illustrated in the accompanying drawing, in which Figure I is a cross-sectional elevation cut-away of an explosive rivet of the prior art inserted in a perforation in two sheets to be connected. Figure II is a round headed rivet according to the present invention, while Figure III shows an improved rivet of the countersunk type.

In Figure I, i represents a rivet of the explosive type, as disclosed in the prior art and used commercially, said rivet being inserted in perforations in the' superposed metal sheets 4 and 5. The rivet shown has a head 2 and ashank 3, and a cavity 6 extending into the shank and opening from the shank end. Into this cavity an explosive charge 1 has been loaded, this charge being positioned so that the greater part of it is slightly below the far surface of sheet 5. When this charge is brought to explosion by the application of a heating surface to the head of the rivet, the'force of the explosion causes the expansion of the walls of the rivet so'that the metal sheets are held firmly together.

In Figure II, a modified rivet according to the present invention is shown, adapted to be inserted through sheets of material in the manner shown in Figure I. The round head of the rivet is designated again by 2 and the shank by 3. This rivet likewise has a cavity 8 entering through the shank, into which the explosive charge I is loaded. This rivet differs in that the cavity is made up of two portions, one of larger diameter 8 and 1 an elongated portion 9 of considerably smaller diameter, this latter part extending substantially to the head of the rivet. With such a cavity design, not only is there explosive in the larger diameter portion that acts to hold the sheets together on explosion but there is also explosive in the narrower, extended portion that blasts the rivet metal into tight connection with the sheets substantially throughout a great part of their entire thickness.

In Figure III, a countersunk type rivet has the head 2 and the shank 3, with a cavity 6 therein. Again'the explosive charge is positioned in both the larger and the smaller diameter portions, 8 and 6, respectively, so that an advantageous riveting effect is secured.

The rivets of the type described in the foregoing may be made of various metals, the'only requirementbeing that said metal'possesssufiicient ductility to allow satisfactory expansion of the walls without rupture.

alloys are applicable, the rivets used in airplane construction, one of the most important fields of use, are generally of aluminum or its alloys.

The size of the rivets will, of course, depend on the thickness of the plates to be secured but a common sized aluminum rivet may have a head spread of 0.3 to 0.4 in. and an over-all lengthof 0.2 to 0.5 in. With what is designated as a in. rivet, for example, having a shank diameter of 0.202 in., a suitable diameter of the main cavity in the shank will be 0.101 in. and that of the extended cavity 0.052 in. We find it important to have the diameter of said-main portion'of the cavity between 0.4 and 0.6 of the shankdiameter. The extended portion of the cavity of narrower opening should have a diameter equal to between 0.2 and-0.4 of that of the shank. The depth of the cavity should be sufiicient generally to have it go substantially to the head of the rivet, in order to obtain maximum efiiciency, but should not be enough to 1eave a deficiency or" metalat the headend so that dimplingor eruption will occur there when the charge is eX- ploded.

In loading the rivets according to our invention, we find it desirable to press the charges to a suitably high density, depending on the type of explosive used. Greater uniformity of density results in the case of the extended cavity rivets of our invention when the loading and pressing are done in at-least two operations. In order to facilitate loading and promote uniformity in density, we find it desirable to have the walls of both larger and smaller portions of the cavity generally parallel to the longitudinal axis of the'rivet. Moreover, the cavity as a whole should be generally stream-lined in contour; that is to say, there should be no connecting walls between the main and the extended'portions that are at right angles to said longitudinal axis. While this is less essential with double pressing of the combined charges, such adesign is'rstill: desirable; in order to avoid dead-end corners.

Various types of explosive charges may be used in the rivets of the present invention. One suitable explosive, for example, may comprise a blend of lead azide and tetrazene in a 90-10 ratio. We find a very desirable loading to'be a mixture of aluminum powder, nitromannite and tetrazene, such as a 48-27-25 proportion of these respective ingredients. With such a blend, a density of charge of 1.6-1.9 may be satisfactorily used. It will be understood, of course, that the charges in the larger and smaller diameter cavity portions may differ in their respective compositions, if so desired.

The rivets of the design and arrangement described in the foregoing possess superior char While such metals as copper, brass, Monel metal and various steel acteristics to those of the prior art explosive rivets. When, for example, the former type was fired in slightly oversize holes, a condition that makes for convenience and rapidity of inserting the rivets in place, insufiicient rigidity of connection frequently resulted. While the tensile and shear strengths were ordinarily satisfactory, the joint tightness was less than desired. With the improved rivet of the present invention, however, the joint tightness is markedly increased under such conditions and suitable rigidity is obtained. The feature of a cavity comprising a main portion and an extended portion of smaller diameter has the advantage over a cavity of the'same'total length but of the larger diameter throughout in that the latter type sacrifices shear strength because of the decreased body of metal in the rivet. Our improved rivet, moreover; is superior to one having the same total length of cavity but of the smaller diameter in-having a larger amount of explosive at the position where substantial. bulging-oftherivet walls is desired, whereby a more secure fastening results.

While the invention has been described adequately and at length in the foregoing, it will be appreciated that many variations may be introduced in details of design and arrangement and conditions of loading, without departure fromthe spirit of the invention. We intend to be limited, therefore, only by the following claim;

We claim:

An-explosive rivet for securing together superposed objects whereinthe rivet is positioned within aligned holes of the superposed objects-.- so that the rivet head is in contact'with the outer surface of said objectsand a'length of the rivet shank projects beyond the' inner surface of saidobjects, said rivet comprisinga head'anda shank, a centrally-disposed cavity extending-mmgitudinally through said shank, said cavity con* sisting of a main portion open at the end of the" shank opposite the head andhaving a diameter of from 0.4 to 0.6 times'that of the shank, the" length ofsaid main portion being greater than the length of the shank projecting b'eyond'the" inner surface of the superposed objects, and a second portion of said cavity extending from said main portion substantially to the juncture'o'f-the' shank -and'the head, said second portion'ha'ving a'diameter of'from to that of the 'mainportion; and a detonating explosivecharge within-- all of said second portion and that art of the"- main portion adjacent the second portion to a point slightly beyondthe inner surface of the superposed objects.

LAWTON A'. BURROWSI WALTER E. LAWSON.

REFERENCES CITED- The following references are of record in the" file. of this patent:

UNITED STATES PATENTS Number Name Date 1,286,382 Mead Dec. 3, 1908" 1,400,401 Allan Dec. 13, 1921 2,080,220 Butter et a1 May 11, 1937 2,378,118 Widrich June-12, 1945 2,387,742 Burrows Oct. 30', 1945 2,398,633 Gazada Apr. 16', 19 16 FOREIGN PATENTS Number Country Date 467,515 Great Britain Jun'e 17, 1937 

